Extensive research has been devoted to the development of degradable tissue scaffolds to fill bone, cartilage or soft tissue defects (Hollister, 2009). The scaffolds that have been developed are generally custom designed and prepared for a defect in a particular individual, are prepared in standardized sizes, or are initially flowable so the scaffold can be injected to fill the tissue gap. For defects that are variable in size, for example a defect in a mandible or long bone due to tumor resection or injury, the scaffolds must be custom designed to fit the defect. This is an expensive, time consuming process that can preclude the use of scaffolds in favor of more traditional approaches such as the grafting of free flap autografts.
Modular orthopaedic implants that can be expanded have been described (see e.g., U.S. Pat. No. 7,481,841, describing a metal prosthesis that may be adjusted via a radio signal; U.S. Pat. No. 7,468,078, describing a modular hip prosthesis with different ball and stem; U.S. Pat. No. 7,455,695, describing a femoral stem modular prosthesis with interlocking nut; U.S. Pat. No. 7,453,263, describing a modular femoral head and neck prosthesis; U.S. Pat. No. 7,309,361, describing a coupled metallic tibia and femoral implant with resorbable lining; and U.S. Pat. No. 7,297,164, describing a modular knee prosthesis with tibial and femoral components broken into medial and lateral sides. But such modular orthopaedic implants have generally been made from permanent materials, or at most a combination of a permanent material with a degradable liner (see e.g., U.S. Pat. No. 7,309,361). Furthermore, permanent materials of conventional modular implants do not provide for surface release of biologic factors individually or separately from one or more individual modules.
While permanent materials have a long history of clinical use, they also have significant drawbacks. Firstly, they are radiopaque, which makes evaluating the degree of healing post-operatively difficult. Secondly, there is a large difference between the elastic modulus of the metal implant and that of the adjacent bone. This can cause stress shielding, which in turn can lead to complications including: implant/screw loosening, future instrumentation failure, device-related osteopenia, soft tissue dehiscence, and fracture. Finally, micromotion of the metal device can create wear debris that triggers an inflammatory response. More recently, devices have been composed from non-degradable polymers, most notably polyether-etherketone (PEEK). While these devices do have the advantage of being radiolucent, the mismatch between the modulus of the material and the bone as well as the potential for wear debris still exist.